Pigment chip composition



Patented Dec. 26, 1939 PIGMENT om COMPOSITION David It Wiggam, Kennett Square, Pa., assignor to Hercules Powder Company, Wilmington,

Del., a corporation oi Delaware No Drawing. Application August 1 5, 1936,

Serial No. 96,319

My invention relates to an improved method for grinding'pigments and to the product thereof. More particularly, it relates to a method for grinding pigments in ethyl cellulose and to the 5 product thereof. I

In the production of pigmented lacquers, enamels, and paints it'is necessary to grind the pigment into the vehicle to secure complete wetting of the pigment and to breakup the aggregates of. the pigment particles. Such grinding is ordinarily done by suspending the pigment in a fluid vehicle which forms a part or all of the finished coating composition and then grinding this suspension in a ball mill or a. burr mill. This is a time consuming and expensive operation.

Heretofore it has been proposed to reduce the time and expense of this operation by grinding pigment with plasticized nitrocellulose containing a small amount of a volatile solvent to provent for the nitrocellulose adds to the fire and explosion hazard of the operation, since the solvents used are highly inflammable in nature. The number of pigments which can be used in the production of pigment chips is limited, since pigments which are oxidizing in character cause fires and explosions in the grinding operation.

-l0- The use 01. nitrocellulose pigment chips is further restricted by the incompatability of nitrocellulose with many film-forming materials, so that their use is practically restricted 'to'pigmented nitrocellulose lacquers. 45 An object of my invention is to provide a pigment chip which can be used in awide variety of different types offinishes and which may contain any of the usual protective coating pigments. I 50 A further object of my invention is to provide a method for the production of. pigment chipswhich practically eliminates risks from fire and explosion during-the grinding operation, which eliminates any necessity for the use of an inflammable volatile solvent in the grinding operation, 5 which allows the use of any known commercial pigment, and which will produce complete dispersions of even the more diflicult dispersible pigments in a comparatively short grinding period.

The product in accordance with my. invention 1 comprises solid colloided ethyl cellulose contain-' ing a high percentage of finely dispersed pigment. The colloided ethyl cellulose may, if. desired, contain either a solvent or a non-solvent plasticizer. The ethyl cellulose contained therein 15 may be any of the usual commercial viscosity types. Thus, a high, medium, or low viscosity type may be used as desired. The ethoxv content of the ethyl cellulose may be within the range of about 42% to about 54% by weight, and will preferably be within the range of about 46% to about 49.5% by weight.-

The product in accordance with my invention may contain any of the numerous pigments suitable for use in protective coatings, such as, for example, zinc oxide, zinc sulfide, lithopone, ti-

taniumdioxide, antimony trioxide, carbon black, iron blue, chrome yellow, chrome green, cadmium Qred, toluidlne toner, para toner, etc.

The product in accordance with this invention will contain a pigment .or a. mixture of pigments in amount substantially in excess of that used in a protective coating or molding composition, and

is intended for use as an intermediate in the production of protective coating and molding 5 compositions. In fact,- nzy new product will be found unsuited for use per se as a protective coating or molding composition due to its high pigment content.

from about 10% to about 20% pigment by weight of the finished pigment chip, less than the maximum amount which can be dispersed. When the maximum amount of pigment is used it will 50.

'and incompletely in solvents. The practical up- TABLE I Practical Maximum maximum Percent Percival Carbon black (Super spectrabrand) rome ye ow Zinc oxide 85 80 Ordinarily it will be desirable that the product in accordance with this. invention contain an amount of pigment near the upper practical limit. However, for certain uses, and with certain pigments it is desirable to use somewhat less than this amount. In any case, the amount of pigment contained in my product will not be less than about 0.4 of the maximum percentage that can be uniformly dispersed, and usually -not less than 0.5 of the practical maximum percentage. I

It will be appreciated that it is impossible to set a definite limitation of the range of percentages by weight of pigment, which the product in accordance with my invention may contain, which will cover the useful range for all pigments, because of the wide variation in the oil-absorption values and the specific gravities of different pigments, and consequently the useful ranges vary widely with different pigments. The product in accordance with this invention will in all cases contain substantially greater proportions of any given pigment than can be used in an enamel or molding plastic.

A variety of solvent and non-solvent plasticizers may be used in the product in accordance with my invention. Solvent plasticizers which may be used are, for example, tricresyl phosphate, tributyl phosphate, dibutyl phthalate, bu-

tylphthalyl butylglycollate, methylphthalyl ethylglycollate, chlorinated diphenyl, hydrogenated alkyl abietates, triethyl citrate, etc. Non-solvent plasticizers which are suitable are castor oil, butyl stearate, neutralized hydrogenated rosin oil,

etc. I prefer to use the least volatile of the solvent plasticizers. Tricresyl phosphate is particularly useful.

I the plastic mass of colloided ethyl cellulose. Any

mill suitable for working stifi plastic masses is suitable for this purpose, as, for example, a differential two-roll mill, a mixer of the nature of a Banbury mixer as described in U. S. Patent 1,523,387, etc. 5

A solvent or non-solvent plasticizer may be added to the ethyl cellulose in the colloiding operation as desired. Unplasticized ethyl cellulose produces tougher plastic and requires a higher working temperature than when plasticlzed witlia solvent plasticizer and it will be found that a pigment can be completely dispersed in a shorter time in the ethyl cellulose when a solvent plasticizer is not present. Non-solvent plasticizers will be found to have very little or no effect on the 15 working temperature of the plastic. The presence of either a solvent or a non-solvent plasticizer has an undesirable effect upon the solubility of the finished pigment chips when containing certain pigments. Thus, for example, I have found that the presence of a solvent plasticizer decreases the solubility of carbon black and iron blue pigment chips, but had practically no effect on the solubility of zinc oxide and chrome yellow pigment chips.

When using pigments which are discolored at the normal colloiding temperature for ethyl cellulose, the colloiding temperature may be lowered and pigment discoloration avoided by the addi- 30 tion of a solvent plasticizer to the plastic.

The temperature at which the ethyl cellulose is colloided and the pigment dispersed therein in the method in accordance with this invention will depend upon the amount of solvent plasticizer used. In the absence of a solvent plasticizer, an operating .temperature'withln the range of about C. to about 150 C. may be used. I have found that a temperature of C. is ordinarily satisfactory. The required operating temperature will be found to decrease as the amount of solvent plasticizer contained is increased. The optimum temperature for a particular composition may be readily established by progressively raising the temperature of the mill as the ingredients are being worked and observing their behavior.

The time of milling required to produce pigment chip in which the pigment is completely and uniformly dispersed will depend upon a number 50 of factors, such as pigment used, size of batch, efficiency of the mill, and various other operating conditions. ditions it will be found that the particular pigment used has a marked influence upon the time 55 required. I have found that pigments which are diificult to grind may be completely and uniformly dispersed under optimum working conditions in less than thirty minutes, while a pigment which is easily ground may be completely 60 and uniformly dispersed in less than five minutes.

When operating under optimum con In following the method in accordance with When using a mill of The products and process in accordance with.75

this invention are further illustrated by the following tables:

' TABLE II Cannon Bmcrr Pramnn'r GBINDB l 5 Two-roll mill v Formula No 1 i 2 R 4 a Eth l cellulose Lot 218 (low vis- 10 56 48 35 28 18 14 12 21 1 19. 7 30 40 50 60 70 Pigment in chip percent 30 40 50 55 60 Temperature oi back roll C 115 125 135 135 135 Temperature of front roll C 95 100 125 v 135 135 15 Total time of grinding. miniltes 26 26 26 I 10 10 15 Good head, no Good bead, slight Good bead, dull, Short bead, losing Fell from rolls in plasticizer loss. plasticizer loss. co 11 Si d a re bl e plasticizer so- 10 minutes.

. plasticizer loss, rapidly that causing ingrinding was creased shortdiscontinued ness of head. alter 10 minutes. 20

Comment: Complete dispersion of pigment within 26 minutes.

TABLE HI CARBON BLACK PIGMENT Games Two-roll mill 25 Formula No i a 3 4 5 Formula No c 7 s 9 10 Ethyl cellulose lLot 222 (low viscosity). 7O 56 49 42 Ethyl cellulose Lot 222 (low viscosity) n Ethyl cellulose Lot 227 (low viscosity) 42 Ethyl cellulose Lot 225 (low viscosity) o0 Tricresylphosphate 14 21 28 28 Ethyl cellulose I. G. (low viscosity). Super Spectra carbon black 30 30 30 30 30 Tricresylphosphate .r. Pigment in chip 30 30 30 30 30 Baker's #15 heavy bodied castor oil Temperature of back roll. 135 110 100 100 100 Abietic acid (commercial) r. Temperature of front roll. 125 100 95 95 95 Super Spectra carbon black Total time of grinding "minutes" 25 25 25 25 25 Pigment in chip percent 30 3O 30 30 30 3,. Temperature of back rol1 100 130 100 100 Temperature of front roll. 95 115 95 95 Total time oi grinding minutes 25 25 25 50 Comment: Pigment added water wet. Good bead in every case. Comment: Additional grinding time used for #10 not necessar No plesticizer loss. Abietic acid used in #9 as a wetting agent. The castor oil used in 8 was absorbed by pigment and grinding was then similar to #1, 40 V which contains no plasticizer. g0

TABLE IV ZINC OXIDE PIGMENT GBINDS Two-roll mill Formula No r 1 2 3 4 5 Ethyl cellulose Lot 222 (low viscosity) r. I 64 45 35 26 18 Dibutylphthalate 16 l6 15 14 12 120 133 15(5). 1% 152 Good bead. Good bead. Slight short- Very short E x tremely.

ness of bead. bead. short bead.

Comment: Plasticizer was lost from all mixtures during grinding, indicating dibutylphthalate to be less desirable than tricresylphospliate. Complete dispersion is less than 5 minutes in every case. Pigment added water wet. Pigment ground with exceptional ease.

TABLE V IRON BLUE PIGMENT Games Two-roll mill n Formula No 1 2 3 4 5 Ethyl cellulose Lot 218 (low viscosity) 48 32. 5 (m Ethyl cellulose Lot 222 (low viscosity) 24 21 6-) Ethyl cellulose I. G. (low viscosity). 48 Tr eresylphosphete 12 17. 5 16 21 12 Chinese blue A1835, 40 5O 60 78 Non-brcnzing blue X882 40 Pigment in chip percent. 40 50 60 65 40 1 Temperature of back roll C 115 115 120 125 115 Tem erature of front roll C 100 105 100 Tot time of grinding minutes 26 26 26 5 30 Good bead. Good bead. Slight short- Fell from rolls Slight shortness ofbead. int flve minness of bead.

u es.

Comment: No plasticizer was lost from these mixtures. Complete dispersion of pigment within 26 minutes. Ifigment added water wet. 7

Chrome green Formula N o Ethyl cellulose I. G. (low viscosity) pounds" Tricresylphosphate do Zinc oxlde do Chrome yellow--. do

Chinese ue do Pigment in grind... percent Temperature of mill TABLE VI CHnomc YELLOW Premmr Gnmns Two-roll mill Formula No 1 2 3 4 5 6 Ethyl cellulose Lot 222 (low viscosity) 80 64 45 35 26 18 'lricresylphosphate 20 16 15 15 14 12 Chrome yellow 100 120 140 150 160 170 Pigment in chip percent... Temperature of back roll.-- .C 115 115 115 115 116 125 Temperature of front roll... C.. 100 .100 100 100 100 Total time of grinding .minutes 26 26 26 ,26 26 26 Good head. Good bead. Good bead. Slight short- Bead some- Bead someness of bead. what short. what short.

Comment: No plesticizer was lost from these grinds. Pigment added water wet. Complete dispersionot pigment within 5 minutes.

Iigment ground with exceptional ease.

TABLE VII Mrscmsnnons PIGMEN'I Games Two-roll mill Formula No 1 2 3 4 5 6 7 Ethyl cellulose I. G. (low viscosity) Ethyl cellulose I. G. (medium Super S eetr'fihhilY Chinese blue A-1835 Titanium dioxide Zinc oxide Chrome yellow A-548 Tricresylphosphate. 00 Pigment in chip .3 Temperature of back oll C 125 135 135 135 135 135 135 Temperature oi front roll C 125 110 110 110 110 110 Total time of grinding mlnutes 10 25 25 5 5 5 20 Good bead. Short head. I Short bead. Slight short- Short bead. Short bead. Slight shortness oibeed. ness of head.

TABLE VII-CONTINUED MISCELLANEOUS Promnn'r GmNns Two-roll mill Formula No I 8 9 10 ll 12 13 Ethyl cellulose l. G. (low viscosity) 4 2 24 74 74 Ethyl cellulose I. G. (high viscosity). Super Spectra carbon black Non-bronzing blue X-882 Chrome yellow A548 Slight short- Slight short- Slight shortness of head. ness 0! head. ness oi bead.

Short bead.

Good bead.

TABLE VIII PIGMENT Gnmns Banblu'y mixer (midget size) cellulose lacquers, varnishes, enamels, paints,

printing inks, wax crayons, etc. from easily wetted pigments such as chrome yellow and zinc oxide which are easily dispersed in solvents.

plete solution.

Comment: All grinds were sheeted on a differential two-roll mill. In every case the mill could have handled a higher percentage of p1g ment.

The product in accordance with this invention is useful in the production of pigmented nitro- Chlps prepared The pigment chips in accordance with this invention can be used'in all lacquer formulas which contain 15 parts of resin or less to 10' parts of nitrocellulose, including those formulated with resins which are incompatible with ethyl cellulose alone. The pigment chips, in accordance with this invention can be used to pigment lacquers having a high resin content, as, for example, 20 parts or more of resin to 10 parts of nitrocellulose when formulated with resins compatible with ethyl cellulose The pigment chips, in accordance with this invention, will be found to give exceedingly smooth pigmented compositions, when used in their formulation, even when containing difflculty dispersable pigments. This is due to the exceedingly complete and uniform dispersion of the pigment which can readily be obtained in an ethyl cellulose plastic.

It will be understood that the details and examples hereinbefore set forth are illustrative only, and that the invention' as herein broadly described and claimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

1. A method of producing a pigment chip which consists of milling a mixture that is substantially non-volatile at normal room temperatures and that requires a milling temperature of above about 100 C. to efiect colloiding, said mixture comprising ethyl cellulose and a pigment within the range of about 40% to about 90% by weight of the maximum amount which can be dispersed in the ethyl cellulose as determined by a shortness of bead while milling at the temperature at which the ethyl cellulose is colloided from about 100 C. to about 150 C. until the pigment is uniformly dispersed throughout the resulting ethyl cellulose colloid.

2. A method of producing a pigment chip which consists of milling a mixture that is substantially non-volatile at normal room temperatures and that requires a milling temperature of above about 100 C. to efiect colloiding, said mixture comprising ethyl cellulose and a pigment within the range of about 40% to about 90% by weight of the maximum amount which can be dispersed in the ethyl cellulose as determined by a shortness of bead while milling and a plasticizer in amount and so proportioned as to require a milling temperature of above about 100 C.

3. A method of producing a pigment chip which consists of milling a mixture that is substantially non-volatile at normal room temperatures and that requires a milling temperature of above about 100 C. to effect colloiding, said mixture comprising ethyl cellulose and a pigment within the range of about 40% to about 90% by weight of the maximum amount which can be dispersed in the ethyl cellulose as determined by a shortness of head while milling and a nonabove about 100 C. to effect colloiding, said mixture comprising ethyl cellulose and a pigment within the range of about 40% to about 90% by weight of the maximum amount which can be dispersed in the ethyl cellulose as determined by a shortness of bead while milling and a solvent plasticizer in amount and so proportionedas to require a milling temperature of above about 100 C.

5. A method of producing a pigment chip which consists of milling a mixture that is substantially non-volatile at normal room temperatures and that requires a milling temperature of above about 100 C. to efiect colloiding, said mixture comprising ethyl cellulose and a pigment within the range of about 40% to about 90% by weight of the maximum amount which can be dispersed in the ethyl cellulose as determined by a shortness of head while milling and tricresyl phosphate in amount and so proportioned as to require a milling temperature of above about 100 C. I

6. A method of producing a pigment chip which consists of milling a mixture that is substantially non-volatile 'at normal room temperatures and that requires a milling temperature of above about 100 C. to efiect colloiding, said mixture comprising ethyl cellulose and a pigment within the range of about 40% to about 90% by weight of the maximum amount which can be dispersed in the ethyl cellulose as determined by a shortness of bead while milling and dibutyl' phthalate in amount and so proportioned as to require a milling temperature of above about 100 C.

7. A method of producing a pigment chip which consists of milling a mixture that is substantially non-volatile at normal room temperatures and that requires a milling temperature of above about 100 C. to efiect colloiding, said mixture comprising ethyl cellulose and a; pigment within the range of about 40% to about by weight of the maximum amount which can be dispersed in the ethyl cellulose as determined by DAVID R. WIGGA 

